Insight into a natural Diels-Alder reaction from the structure of macrophomate synthase

The Diels-Alder reaction, which forms a six-membered ring from an alkene (dienophile) and a 1,3-diene, is synthetically very useful for construction of cyclic products with high regio- and stereoselectivity under mild conditions. It has been applied to the synthesis of complex pharmaceutical and biologically active compounds. Although evidence on natural Diels-Alderases has been accumulated in the biosynthesis of secondary metabolites, there has been no report on the structural details of the natural Diels-Alderases. The function and catalytic mechanism of the natural Diels-Alderase are of great interest owing to the diversity of molecular skeletons in natural Diels-Alder adducts. Here we present the 1.70 A resolution crystal structure of the natural Diels-Alderase, fungal macrophomate synthase (MPS), in complex with pyruvate. The active site of the enzyme is large and hydrophobic, contributing amino acid residues that can hydrogen-bond to the substrate 2-pyrone. These data provide information on the catalytic mechanism of MPS, and suggest that the reaction proceeds via a large-scale structural reorganization of the product.     

牙鲆贫血症病毒分离株的特性

用CHSE－214细胞，从患贫血症的牙鲆肾脏组织分离出一株病毒。电镜揭示为无囊膜、6面体、粒子直径约60nm；理化特性表明：病毒复制不受IUdR、BVdU的影响，对氯仿、乙醚不敏感性，热（60℃，30min）、酸（pH3．0，3h）中稳定；可被抗IPNV－Sp、Ab和VR－299株血清中和，其中抗Sp株血清的ND50为1:2560;病毒能在5～30℃增殖，最适为15～25℃；在盐度0．8～2．0％的培养液中，生长无明显差别；在16种鲑科和非鲑科鱼类细胞上，15℃培养1～4d出现CPE；感染细胞丫啶橙染色显示为黄绿色；用BirnavirusYAV株引物，PCR检出该病毒。结果提示该病毒株应属dsRNA的Birnavirus。     

Nuclear Photon Science with Inverse-Compton Photon Beam

Recent developments of the synchroton radiation facilities and intense lasers are now guiding us to a new research frontier with probes of a high energy GeV photon beam and an intense and short pulse MeV γ-ray beam.We discuss new directions of the science developments with photo-nuclear reactions with the inverse Compton γ-rays for studying hadron structure, nuclear structure, astrophysics, materials science, as well as for nuclear technologies.     

Java字节码异常处理中信息流的分析

为提高Java移动代码动态安全验证的准确性和实用性,通过分析Java字节码中异常处理的方式与流程,提出了追踪、记录异常处理中信息流的方法.采用字节码改写技术,将异常处理中信息流的相关数据封装在异常类当中,从而保证了所采取的处理对Java虚拟机的透明性,并进一步提高了动态验证的精度.     

聚合物波导折射率渐变型Spot-size converter设计

围绕光致折射率变化聚甲基苯基硅烷高分子光波导,设计了新型的折射率渐变型Spot-size converter,可有效改善光纤与光波导的端面耦合效率．BPM仿真计算显示,耦合效率由78％提高到91％,为器件制备提供了理论依据．     

HAR1 mediates systemic regulation of symbiotic organ development

Symbiotic root nodules are beneficial to leguminous host plants; however, excessive nodulation damages the host because it interferes with the distribution of nutrients in the plant. To keep a steady balance, the nodulation programme is regulated systemically in leguminous hosts. Leguminous mutants that have lost this ability display a hypernodulating phenotype. Through the use of reciprocal and self-grafting studies using Lotus japonicus hypernodulating mutants, har1 (also known as sym78), we show that the shoot genotype is responsible for the negative regulation of nodule development. A map-based cloning strategy revealed that HAR1 encodes a protein with a relative molecular mass of 108,000, which contains 21 leucine-rich repeats, a single transmembrane domain and serine/threonine kinase domains. The har1 mutant phenotype was rescued by transfection of the HAR1 gene. In a comparison of Arabidopsis receptor-like kinases, HAR1 showed the highest level of similarity with CLAVATA1 (CLV1). CLV1 negatively regulates formation of the shoot and floral meristems through cell-cell communication involving the CLV3 peptide. Identification of hypernodulation genes thus indicates that genes in leguminous plants bearing a close resemblance to CLV1 regulate nodule development systemically, by means of organ-organ communication.     

基于OpenGL的仿人机器人步行仿真研究

已有的仿真建模中,为了减少复杂性,大多将人足模型简化为点或圆弧,这与实际情况相差较远.在C++Builder 6.0环境下利用“Open GL”图形库建立了3D仿人型机器人双足步行仿真系统,用多关节串联机构模拟足部,实现包括由前脚掌支撑、足部转动的多种步态方式,并分析步行中各种步态间的转换,根据机器人脚跟、脚尖与地面接触状态的变化动态切换不同的步态方式,符合人足步行的实际情况,增强了机器人步行的灵活性与拟人性.该系统的控制部分采用位置反馈与正弦驱动相结合的行走控制方法,通过对人足模型的多关节动力学建模,有效地实现了机器人的稳定步行仿真,并实现了步行过程中的实时步态调整.     

利用近红外彩色成像技术监测松萎蔫病 Katsunori Nakamura, Mamoru Takehana, Tsuneo Itagaki, Hayato Tashiro,Kazumasa Ohta,Osamu Nakakita

有效监测患病株方法的缺失是导致对松萎蔫病难以成功控制的主要原因之一。利用航空手段调查该病导致的针叶颜色变化已被证明是一种可靠的方法。为了克服该方法固有的缺点，笔者引用了近红外彩色胶片航拍方法。该项技术在获得正摄航拍图像时，通过图像处理可以增强松针颜色变化，获得较直接拍摄图像更明显的色差。因为图像可以在室内仔细处理，因此能解决飞行时间缺乏等问题。但是，该方法也存在对被压木无法获得其影像而漏检的缺陷。笔者研发的计算机软件可以将目标树标记在计算机图像文件上，并且标记树的地理位置数据和背景航拍图像并传输到装有内置GPS接收器的掌上电脑中，借助软件产生的图像导航定位系统，有利于地面接近标记树，从而可以现场检查和校正标记树的数据，并将修正数据传回至主机。此方法利用最新航拍图像技术建立对每株树处理和管理的连续资料，大大改善了防控松萎蔫病的措施。     

Crystal structure of the human centromeric nucleosome containing CENP-A

In eukaryotes, accurate chromosome segregation during mitosis and meiosis is coordinated by kinetochores, which are unique chromosomal sites for microtubule attachment. Centromeres specify the kinetochore formation sites on individual chromosomes, and are epigenetically marked by the assembly of nucleosomes containing the centromere-specific histone H3 variant, CENP-A. Although the underlying mechanism is unclear, centromere inheritance is probably dictated by the architecture of the centromeric nucleosome. Here we report the crystal structure of the human centromeric nucleosome containing CENP-A and its cognate α-satellite DNA derivative (147 base pairs). In the human CENP-A nucleosome, the DNA is wrapped around the histone octamer, consisting of two each of histones H2A, H2B, H4 and CENP-A, in a left-handed orientation. However, unlike the canonical H3 nucleosome, only the central 121 base pairs of the DNA are visible. The thirteen base pairs from both ends of the DNA are invisible in the crystal structure, and the αN helix of CENP-A is shorter than that of H3, which is known to be important for the orientation of the DNA ends in the canonical H3 nucleosome. A structural comparison of the CENP-A and H3 nucleosomes revealed that CENP-A contains two extra amino acid residues (Arg?80 and Gly?81) in the loop 1 region, which is completely exposed to the solvent. Mutations of the CENP-A loop 1 residues reduced CENP-A retention at the centromeres in human cells. Therefore, the CENP-A loop 1 may function in stabilizing the centromeric chromatin containing CENP-A, possibly by providing a binding site for trans-acting factors. The structure provides the first atomic-resolution picture of the centromere-specific nucleosome.     

Targeted gene correction of α1-antitrypsin deficiency in induced pluripotent stem cells

Human induced pluripotent stem cells (iPSCs) represent a unique opportunity for regenerative medicine because they offer the prospect of generating unlimited quantities of cells for autologous transplantation, with potential application in treatments for a broad range of disorders. However, the use of human iPSCs in the context of genetically inherited human disease will require the correction of disease-causing mutations in a manner that is fully compatible with clinical applications. The methods currently available, such as homologous recombination, lack the necessary efficiency and also leave residual sequences in the targeted genome. Therefore, the development of new approaches to edit the mammalian genome is a prerequisite to delivering the clinical promise of human iPSCs. Here we show that a combination of zinc finger nucleases (ZFNs) and piggyBac technology in human iPSCs can achieve biallelic correction of a point mutation (Glu342Lys) in the α(1)-antitrypsin (A1AT, also known as SERPINA1) gene that is responsible for α(1)-antitrypsin deficiency. Genetic correction of human iPSCs restored the structure and function of A1AT in subsequently derived liver cells in vitro and in vivo. This approach is significantly more efficient than any other gene-targeting technology that is currently available and crucially prevents contamination of the host genome with residual non-human sequences. Our results provide the first proof of principle, to our knowledge, for the potential of combining human iPSCs with genetic correction to generate clinically relevant cells for autologous cell-based therapies.